Conventional pins for a chain have been provided with an abrasion-resistant surface and a tough core part by chromizing pin blanks containing from 0.4 to 0.7% by weight of carbon in a ferrous alloy to form a high-hardness chromium layer at the surface while forming fine crystal grains in the core part, as disclosed in, for example, Japanese Patent Publications No. 57-38669 (1982) and No. 57-60422 (1982).
However, because of the high carbon content of not lower than 0.4% by weight of the pin blanks, plastic working of the pin blanks could not be easily carried out and, upon heat treatment, the hardening effect penetrated into the core part of the pin blanks. Hardening normally reduces the toughness, i.e. rupture strength or cuttability, so that improvement of rupture strength could not be expected.
On the other hand, when the surface of a blank composed of a ferrous alloy with a carbon content of less than 0.4% by weight is chromized, formation of cyrstals of metal carbides in the surface layer is slight and, therefore, a high-hardness surface layer cannot be formed.